General banding in a digital image or video sequence can be caused by coarse quantization of gray scale value or color values and typically gives a “false contour” effect in a smooth region of a picture. In addition, such “false contour” may be affected by various codec compression standards to become more “square mosaic,” i.e., codec banding.
There are several causes for the occurrence of banding artifacts. One general cause is the manipulation or conversion applied to digital images which are quantized near the limit of just noticeable gray scale value or color differences; another cause is the compression of an image or video sequence by various video codec.
Conversional methods such as noise mask or dithering method may result in artificial patterns occurring in an entire image. In recent years, pixel-wise “false contour” detection and removal approaches have been proposed, e.g., US2010/0142808 or US2009/0060375. In these kinds of methods, the detection of banding is performed by calculating the color value offset for each pixel within a region determined by the scale, followed by applying certain criteria to decide yes/no locally to de-banding.
Referring to the above-mentioned related arts, the existing methods mainly explore pixel-wise image gray scale or color differences. Most of the proposed methods do not take into consideration coded block boundaries offset generated by compression codec (i.e., blockiness artifacts), and they do not identify and protect texture region explicitly (i.e., light texture blurring). Furthermore, there is little work on handling “new false contour” occurring in the transition between banding and non-banding region, or the transition between banding region and mono-tone region, respectively.